Chromatography columns may be used in industrial processes to purify process liquids and separate substances of interest from process liquids; typical examples include large-scale preparative purification of fine chemicals and pharmaceuticals, together with biological products.
Industrial-scale chromatography columns typically comprise a hollow, axially vertical tubular housing including a liquid inlet at the upper end and through which the buffer and substances to be separated are dispensed to the media bed located within the cavity of the tube, and a liquid collecting system at the lower end for collecting substances and buffer. The particulate chromatographic media or bed through which the buffer fluid and/or substances to be separated and purified percolates is located between the liquid inlet and collecting system.
An adapter assembly is typically affixed to the upper end of the tubular housing and a base assembly to the lower end where it is bolted to the bottom flanges. Each of these assemblies typically comprises a strong backing plate and a distributor plate which further supports a layer of mesh, sinter or other fluid-permeable media-retaining material which permit process liquid flow into and out of the chromatography bed space or cavity while retaining the bed of particulate medium. To provide adjustability and control of the bed height and bed compression, the adapter assembly is typically made in the form of a piston or sliding adapter in the column tube interior. After the column is charged with bed media, typically through a nozzle, the adapter may be forced toward the bottom of the tube to compress or pressurize the media bed. Generally the base assembly is a fixed structure which is bolted against the bottom flange of the column tube but, in some instances, may also be in the form of a movably slidable piston or adapter.
The backing plate of the base assembly generally acts as a support for the column, being itself supported on legs or some other stand arrangement which allows clearance for outlet pipework projecting beneath the base assembly.
When such a column requires maintenance to, or cleaning of, internal components, such as the valves, seals, meshes/screens, distribution systems etc., heavy lifting gear such as a crane or hoist is necessary to lift the upper end/adapter assembly away from the column tube and the column tube away from the lower end/base assembly as these assemblies can weigh in excess of three tons. The use of heavy overhead lifting equipment to disassemble the column in order to carry out internal maintenance is not desirable. Operator safety is obviously a concern when heavy equipment is lifted overhead and technicians exposed below. Furthermore, alignment structures are required to keep the column and its base/adapter assemblies axially aligned as they are separated from each other, to avoid damage to the precision components.
The presence of such alignment and lifting structures imposes significant obstructions around the tube and need to be carefully laid out to provide sufficient clearance at some point of the circumference for insertion/removal of the internal components. Furthermore, the requirement to use heavy lifting equipment imposes constraints on housing such columns, sufficient overhead space and support being required to accommodate hoists or cranes. As many chromatography columns are now run in “clean” environments, to avoid microbiological contamination, where it is extremely difficult to accommodate overhead equipment, the requirement of moving the column to another room for disassembly and maintenance is problematic. This problem is exacerbated by the need to clean and verify the column before returning it for use to the clean environment.
U.S. Pat. No. 6,736,974 addresses some of the above problems by providing a column which is capable of lifting the adapter assembly above the column tube and/or raising the column tube above the base assembly by means of an hydraulic system which is integral to the column.
However, the system described in U.S. Pat. No. 6,736,974 has significant disadvantages associated with it by virtue of its design. As can be seen from FIGS. 4 and 5 of U.S. Pat. No. 6,736,974 and described in column 4, lines 63-66 of that document, in order to remove the distributor plate (31) and/or mesh (28/60) from the interior of the column, the operator must work within the centre of the drum (18) to access and remove the fixing nut (30) which secures these component parts. As industrial columns typically have diameters ranging from about 200 mm to 2000 millimetres, this means that the operator must work below a suspended or supported load to unscrew the nut. This clearly poses a significant safety risk to the operator, particularly where the operator's arm or head is exposed below the suspended or supported load.
Furthermore, once the column tube/cylinder or adapter assembly has been raised from the base assembly or tube, respectively, removal of the heavy bed support plate, distributor plate or mesh from the column can only be accomplished by tilting the plate or mesh at an angle to negotiate the hydraulic drive pistons or safety rods. This can clearly be seen from, for example, FIGS. 3, 4 and 5 in which the distance between any two safety rods (69) or between any two hydraulic pistons (36) is less than the diameter of the mesh (28/60) or distributor plate (31). The same problem would exist for the base or adapter bed support plate (not shown). Removal of these internal components, which could weigh in excess of 100 kg, requires considerable manhandling by the operator and necessitates their being exposed below the suspended column or adapter assembly. Once again, this represents a significant safety risk for the operator.
The task of physically removing the heavy bed support plate or distributor plate, as described in U.S. Pat. No. 6,736,974, must be carried out by an operator, there being no disclosure of the use of any lifting aid to assist in this task. The configuration of the hydraulic pistons and the safety rods, and the need to tilt the plates in order to avoid hitting these supporting structures in withdrawing the plates from the column, would require the design of a bespoke lifting device.
WO 2005/056156 (Euroflow (UK) Limited) also discloses a column which can be accessed for maintenance without the need for a crane or hoist. The column is designed such that the tube and the base assembly can be separated by means of hydraulic drive cylinders to provide an access space between them to conduct maintenance or service on the base assembly. The piston of the adapter assembly can be advanced through the column tube to expose it at the open end of the column tube, i.e. in the space between the tube and the base assembly, for maintenance.
However, as is evident from this document (for example, FIGS. 19 and 20 and related description on page 23) access to release the fastening screws retaining the mesh in place is provided by the space between the tube and the base assembly. Removal of the meshes necessitates the operator being exposed to a suspended load while retaining screws are removed. Furthermore, the distance between any two drive cylinders for maintenance access is greater than the diameter of the bed support assembly (see, for example, FIG. 7), which requires the operator to manhandle and tilt the mesh or bed support when removing or replacing it. Maintenance of the column thus imposes a significant safety risk for the operator.
Accordingly, a need exists to improve the maintenance methods available for chromatography columns by providing columns which are safer and easier for operators to use and which do not expose them to a suspended or supported load.